The present invention relates to the construction of the intake passageway of an engine, particularly to the intake passageways in an intake manifold and head for an internal combustion engine.
The intake ports of a head and intake runners of an intake manifold operate most efficiently at one speed of the engine within the designed range of speeds for the engine. If this design speed is relatively low for the range of speeds, the engine will operate efficiently at low speeds, but at high speeds the passageways will "choke", that is they will not be able to provide sufficient flow of fluids to the engine for efficient operation. On the other hand, if the design speed for the passageways is relatively high for the speed range, the engine will operate efficiently at high speed, but at low speed it will operate quite inefficiently and rough. It is well known to provide after market intake manifolds that will provide for increased horsepower and fuel efficiency at high speeds, but the low speed or street use operation suffers.
For the standard "small-block Chevrolet engine", the intake runners for two adjacent cylinders are parallel to each other and share a common dividing wall in the head. It has been a common practice to grind the outer walls of this intake runner, but the amount of enlargement is really restricted by adjacent cooling chambers, push rods and necessary wall strength. It is also common to grind away the sides of the dividing wall to make it thinner. Each of these procedures will raise the speed at which the runners are "tuned" or will operate most efficiently, while at the same time decrease the efficiency for the lower speed range of the engine. This is satisfactory for racing purposes where the engine is run at very high speeds, and very seldom run at low speeds, but it is unsatisfactory for normal usage. Therefore, it is necessary for people who are racing to have one head designed for racing and one head designed for street use, and many people have several different heads depending upon the type of racing or street usage that will in turn determine the speed at which the engine is usually run. It is even known to completely grind away and eliminate the dividing wall within the head so that effectively the adjacent cylinders will share a common runner within the head. This will provide the very high flow volume needed at extremely high speeds, but at a great loss for the remaining speed range of the engine.
The volume of air (actually fuel air mixture for carbureted internal combustion engines, or only air for injected engines, or combustion products for external combustion engines) increases with increased engine speed, and it is easy to understand that the intake runners may be too small to provide this flow of air and it will therefore become "choked". However, the converse is also true that the intake runners may be too large for a lower speed in that the air will tend to be somewhat dead with high inertia, that is at low speeds it is desirable to have a smaller runner so that the velocity of the air may be maintained for efficiency of charging. All of this is well known in the design of intake runners.